The reaction of 2-chloro-1-methoxynaphthalene and 2-bromobiphenylene with 3-cyanophthalides under aryne-forming conditions: convenient synthesis of annular polycyclic aromatic compounds

2-Bromobiphenylene and 2-chloronaphthalene react with 3-cyanophthalides in the presence of LDA or LiTMP to give functionalized benzo[3,4]cyclobuta[1,2-b ]anthracene-6,11-dione and naphthacene-5,12-dione, respectively.


Introduction
Biphenylenes have recently been studied extensively because they can serve as units of new carbon allotropes and can function as spacers and building blocks for functionalized organic materials. 1One of the more important syntheses of functionalized biphenyls involves the intramolecular coupling of benzo-annulated zinca-cyclopentadiene intermediates prepared from 2,2'-diaryls with ZnCl 2 . 2 During the course of our studies on the synthetic use of aryne reaction, we have prepared a wide variety of functionalized polycyclic quinones from the reaction of haloarenes with 3-lithiophthalides in the presence of sterically hindered bases such as LDA and LiTMP. 3It occurred to us that 2-bromobiphenylene might undergo similar reactions to give functionalized annulated biphenyls.Although 2-bromobiphenylene can, in principle give two benzynes, i.e., 1,2-dehydro-and 2,3-dehydro-biphenylene, our calculations have shown the 2,3-intermediate to be 4.47 kcal/mol more stable than the 1,2-isomer.The relative stability of 1,2-and 2,3-dehydrobiphenyl were calculated with complete optimization of all geometric variables using the standard AM1 procedure 4 incorporated in version 3.1 of the Spartan Package. 5 Furthermore, the latter, being symmetric, would give a single aryne product.

Experimental Section
General Procedures.Melting points were taken on a Mel-Temp apparatus and are not corrected.NMR spectra were recorded on a 400 MHz spectrometer: chemical shifts were related to TMS as internal standard.

ISSN 1551-7012
Chemicals were purchased from commercial sources.LDA and BuLi were purchased as solutions in hexanes.
The glassware heated at 125 o C in an oven overnight prior to use.Benzyne reactions were done under an atmosphere of dry O 2 -free N 2 contained in a balloon possessing a needle protruding through a rubber septum attached to one of the reaction flask necks.

procedure for the reaction of haloarenes (2 and 7 )
with 3-cyanophthalides (4a-c).In a flamedried flask flushed with N 2 , LDA (15 mmol) was prepared by adding 6 mL of n-BuLi (2.5 M in hexanes) to a solution containing diisopropylamine (15 mg, 15 mmol) in THF (30 mL) at -70 o C.After stirring for 10 min, 5 mmol of the appropriate nitrile (4a-c) in 30 mL of THF was added and the temperature allowed to warm to -40 o C. At this point, 5 mmol of the haloarene (2 or 7) in 30 mL of THF was added over a period of 20 min while maintaining the temperature between -30 to -40 o C.After the addition of the haloarene, the resulting mixture was allowed to warm to r.t.where it was stirred for an additional 3 h.The resulting dark reddish solution was quenched with 30 mL of sat.NH 4 Cl and the THF removed by rotary evaporator.The residue was extracted with CH 2 Cl 2 (3 × 20 mL).The CH 2 Cl 2 fractions were combined, washed with 25 ml of 5% HCl, then brine, then dried (Na 2 SO 4 ) and concentrated (rotary evaporator) to provide a dark viscous liquid.The liquid was purified by flash chromatography (silica gel) using hexane/acetone (19:1) as eluent to give a solid product which was further purified by recrystallization from CH 2 Cl 2 -hexane.The physical properties of the products are given below.Benzo[3,4]cyclobuta[1,2-b]anthracene-6,11-dione (8a).Yellow powder, mp 218-219 0 C. IR (KBr) ν 1684 cm -1 . 1 H NMR (CDCl 3 ) δ 6.81 (d, J = Hz, 2 H), 6.92 (m, 2 H), 7.32 (d, J = 8.0 Hz, 1 H), 7.73 (m, 2 H), 7.79 (d, J = 8.